JPH1190179A - Method for detoxifying nitrogen trifluoride and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat NF3 in a safe and efficient manner by passing NF3 -contg. waste gas and a reducing gas as a down flow through a catalyst bed heated to a specified temp. and supplying water to a position kept at a specified temp. under the catalyst bed. SOLUTION: When NF3 -contg. waste gas is detoxified, a waste gas introducing pipe 1 and a reducing gas introducing pipe 2 are connected to the top of the body 5 of a reaction tube with a catalyst bed 3, a water introducing pipe 4 and an exhaust port 6. The waste gas is passed as a down flow through the catalyst bed 3 heated to 200-800 deg.C and water is supplied from the lower water introducing pipe 4 to a position kept at >=120 deg.C under the catalyst bed 3. The gas passed through the bed 3, together with the water, is allowed to flow downward, NH4 F.HF, etc., are dissolved in the water and the water is discharged from a discharge pipe 9. The exhaust port 6 is put in a liq. in a receiver 8, the NH3 and HF in the gas are absorbed in the liq. and the remaining gas which does not affect the human body and environment is discharged into the air.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the nitrogen trifluoride gas about abatement method and detoxification apparatus (hereinafter, referred to as NF _3).

[0002]

2. Description of the Related Art At present, it is well known that restrictions are imposed on chlorofluorocarbons and CO ₂ which have a bad influence on the global environment, and NF ₃ is also a substance which is not easily decomposed in nature. In recent years, a large amount of NF ₃ gas has been used as a cleaning gas or an etching gas in semiconductor manufacturing. However, since it is toxic, it is necessary to remove NF ₃ remaining in the exhaust gas.

[0003] One method to remove the NF _3, a method using a catalyst is known. These differ depending on the type of catalyst, but those in which fluorine is immobilized on the catalyst have a short catalyst life, and those which become another gaseous fluoride consume the catalyst. Therefore, these methods have a common drawback in that the abatement agent charged in the abatement device needs to be replaced or replenished, which increases the running cost. In addition, a method in which exhaust gas containing NF _{3 is} passed through a column using activated carbon as a catalyst at a high temperature (Japanese Patent Application Laid-Open No. 62-237929) has a result that CF _4, which is one of the causes of global warming, is released. Become.

As another method, a method of decomposing NF _{3 in} a flame such as hydrogen or propane is also known. However, the cost of the apparatus is reduced by troubles caused by misfiring of the flame and various incidental facilities for preventing misfiring. But expensive. NF in yet another way
A method is also known in which a reducing gas is added to an exhaust gas containing No. ₃ and the gas is passed through a heated catalyst layer. However, also in this method, the generated fluoride is a relatively high temperature part under the catalyst layer,
This results in blockage due to consolidation, which hinders the flow of exhaust gas.

[0005]

[0008] The present invention is intended to provide a method of processing a NF ₃ safe, and efficient.

[0006]

Means for Solving the Problems The present inventors have intensively studied a method which can improve the disadvantages of the prior art and can be implemented industrially, and as a result, have improved the method to decompose NF ₃ using a reducing gas and a catalyst. In addition, a detoxification method and apparatus capable of preventing the obstruction of fluoride have been developed.

That is, according to the present invention, an exhaust gas containing NF ₃ and a reducing gas are passed through a catalyst layer heated to 200 to 800 ° C. in a down flow, and then, a position below the catalyst layer kept at 120 ° C. or higher is used. Supplying nitrogen to water. A reaction tube main body having a packed bed of the catalyst and a water introduction port at a position below the packed bed; an introduction pipe for an exhaust gas containing nitrogen trifluoride and an introduction pipe for a reducing gas on the upstream side; The present invention relates to an apparatus for removing nitrogen trifluoride, which is provided with a liquid receiver and a drain outlet pipe, and further includes a catalyst heating heater.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in more detail. The abatement method and abatement apparatus of the present invention are applied to abatement of gas containing NF ₃ such as exhaust gas from a super LSI etching apparatus and exhaust gas of a CVD cleaning gas. This N
Exhaust gas containing F ₃ reacts with reducing gases, abated.

[0009] ensuring safety in the reaction of the reducing gas and NF ₃ is particularly important. This includes reducing gas and NF
Of course, the gas composition is controlled so that the gas mixture ₃ does not form an explosive gas mixture, but it is important that the temperature rise of the reactor due to the heat generated by the reaction be suppressed to an appropriate range.
For this reason, NF ₃ is diluted with an inert gas to 2% by volume or less (hereinafter simply referred to as%), preferably 1.5% or less, more preferably 1% or less before being mixed with a reducing gas. You. As the inert gas for dilution, nitrogen is usually used.

As the reducing gas of the present invention, hydrogen and ammonia are preferably used. Hydrogen chloride is a gas that can reduce and decompose NF ₃ by a reaction, but is not preferable because it easily corrodes the reaction tube. Hydrocarbons are also gas that can be reduced and decomposed, but are not preferred because it generates a CF _4.

The amount of reducing gas is determined by the amount of NF contained in the exhaust gas.
_The stoichiometric value or more than the stoichiometric value is required for ₃ and the acid gas component, preferably 1-2 times the stoichiometric value, more preferably 1-1.2 times the stoichiometric value.

The reaction between NF ₃ and the reducing gas proceeds according to the equations (1) and (2) by means of a catalyst. NF ₃ + 3H ₂ → NH ₃ + 3HF (1) NF ₃ + NH ₃ → N ₂ + 3HF (2)

Although the catalyst used in the present invention is not particularly limited, for example, Na, K, Cs, Mg, Ca, Sr, Ba,
Al, Ga, In, Sn, Pb, Sb, Bi, Cu, Z
n, Cd, Sc, Y, La, Hf, V, Cr, Mn, T
c, Fe, Co, Ni, Zr, Ru, Rh, Pd, A
Examples include metals such as g, Ir, Os, Pt, and Au, oxides, carbonates, sulfates, and fluorides. Among them, Fe, C
o, Ni, Cu, Zn, Ru, Rh, Pd, Ag, I
A simple metal selected from the group consisting of r, Pt, and Au, or a supported catalyst containing these elements is preferable. Note that the carrier used in the supported catalyst, metal oxide or NaF, such as Al ₂ 0 ₃ and ZnO, with a metal fluoride such as CaF ₂ as a carrier, also supporting an active ingredient therein of the present invention Included in the range. Among them, metal fluorides are preferred carriers because the catalyst performance does not change with time due to fluorination. The shape of the catalyst is not particularly limited, but fibrous, spherical,
Any shape such as a tablet shape, a ring shape, and a crushed product (irregular type) can be used.

The reaction temperature of the reducing gas with NF ₃ varies depending on the type of the reducing gas and the catalyst, but is usually 150 to 80.
It is appropriately selected within the range of 0 ° C. Above all, 250-600
C., preferably at 300 to 400.degree. If the reaction temperature is lower than 150 ° C., the reaction cannot proceed at an industrially acceptable rate. If the reaction temperature exceeds 800 ° C., the heat resistance and corrosion resistance of the apparatus will be problematic, and the equipment cost will increase.

As described above, NF ₃ is decomposed by using a reducing gas and a catalyst, and HF generated by decomposition is converted into NH ₃ generated by decomposition or NH ₃ used as a reducing gas.
To form NH ₄ F.HF (ammonium fluoride acid) shown in the formula (3), which adheres to the lower pipe of the catalyst layer, which causes a blockage of the pipe, and the operation must be stopped.

Accordingly, safe and efficient operation is impaired, and regular maintenance management is required, resulting in an increase in management costs. NH ₃ + 2HF → NH ₄ F · HF (3) The present invention is to treat NH ₄ F · HF, which causes blockage of the pipe, by a simple method to prevent blockage.

First, the inventors of the present invention measured the temperature of the pipe at the portion where NH ₄ F.HF adhered, and found that it adhered at a portion lower than 120 ° C. This means that N
This is also a theoretical result from the fact that the melting point of H ₄ F · HF is 125 ° C. Therefore, utilizing the fact that NH ₄ F · HF is soluble in water, NH ₄ F
-Install a water introduction pipe between the parts where HF begins to adhere,
Blockage was prevented by supplying water.

The supply amount of water is 0.1% of the gas volume of NF _3.
The solution is passed through 10 to 10 times, preferably 1 to 5 times the volume. If the supply amount of water is less than 0.1 times the gas capacity of NF ₃ , NH ₄ F
-HF cannot be completely dissolved, and the object of the present invention cannot be achieved. On the other hand, if the supply amount of water exceeds 10 times the gas capacity of NF ₃ , it is not preferable because the cost of treating the wastewater increases.

If water comes into direct contact with the catalyst layer, the shape of the catalyst will change, and the capacity will decrease, so it is not preferable to supply water from above the catalyst layer. Therefore, the exhaust gas containing nitrogen trifluoride and the reducing gas must be flown downflow through the catalyst layer so that water does not directly contact the catalyst layer. NF ₃ decomposed in the catalyst layer is N ₂ , NH ₃ , HF, NH ₄
Changed to F · HF, almost excluding the N ₂ is dissolved in water.

The aqueous solution dissolved in water is collected in a lower receiver and neutralized in a processing step. Therefore, NH ₃ and HF can be removed from the exhaust gas that has come into contact with the catalyst layer and water by the apparatus described below, and can be directly discharged to the atmosphere.

Next, the device of the present invention will be described. N
An exhaust gas inlet pipe and a reducing gas inlet tube containing F _3, connected to the upper part of the reaction tube body. The reaction tube main body is composed of a catalyst packed layer, a water introduction tube, and a discharge port, and exhaust gas flows through the catalyst layer in a down flow. The gas that has passed through the catalyst layer flows downward together with the water supplied from the lower water introduction pipe. This water is N
H ₄ F, HF, etc. are dissolved, collected once in a receiver, and discharged from a drain pipe.

The treated gas can be safely vented in several ways. One, as shown in FIG. 1, is to cause the liquid in the receiver to immerse the outlet of the reaction tube main body, thereby absorbing NH ₃ and HF in the gas and removing the gas that does not affect the human body or the environment. It is a method of releasing to the atmosphere.

As a method of collecting the processed gases and guiding them to another path, a structure as shown in FIG. 2 may be employed. That is, the outlet of the reaction tube main body has a double tube structure of an outer tube and an inner tube, the outer tube is made longer than the inner tube, and the outer tube and the inner tube are immersed in the liquid in the receiver. Is a method in which a discharge tube is provided in a part of.

Generally, stainless steel, nickel, and Hastelloy are used for the material of the reaction tube main body, and stainless steel, nickel, or a resin other than soft vinyl chloride and nylon can be used for the material of the receiver. A heater equipped with a temperature controller such as a mantle heater or a sheath heater is used for heating the catalyst packed bed.

[0025]

The present invention will be described in more detail with reference to the following examples. Example 1 The apparatus used is the same type of apparatus shown in FIG. 2, and the catalyst packed bed has an inner diameter of 4.1 mmφ × length of 76 mm (1 c
m ³ ). The main body was made of nickel, and the receiver was made of polyethylene resin. 1.6 g of a catalyst composed of 30 wt% of copper oxide and 70 wt% of calcium fluoride having a particle size of 0.5 to 1 mmφ was filled in the catalyst packed layer (3). Receiver (8)
, And 10 cc / h of city water is passed through the water inlet pipe (4), and the catalyst packed bed (3) is heated by the heater (10).
Heated to 00 ° C, NF ₃ 1% from exhaust gas introduction pipe (1),
Exhaust gas consisting of the remaining nitrogen was supplied to the reaction tube main body (5) at 1 L / h and hydrogen was supplied to the reaction tube main body (5) at 50 cc / h from the reducing gas introduction pipe (2). The drainage was collected from the drainage pipe (9) while maintaining the temperature of the water inlet pipe at 130 ° C. The treated gas was discharged to a gas discharge pipe (7) through a discharge port (6) having a double pipe structure. 24 hours and 48 hours after the start of the supply, the exhaust gas at the outlet from the gas discharge tube (7) was analyzed by gas chromatography, and NF ₃ was not detected. Also, there was no blockage by NH ₄ F · HF.

Example 2 Using the same apparatus as in Example 1, the catalyst used was 0.5 to 1
3 wt% of palladium with particle diameter of mmφ, 97 wt% of alumina
% Of the catalyst. Water was previously stored in a receiver, 5 cc / h of city water was passed through a water inlet tube, the catalyst packed layer was heated to 150 ° C. by a heater, and 300 cc of an exhaust gas having the same composition as that of the example was discharged from the exhaust gas inlet tube. / H Ammonia was supplied to the reaction tube body at a rate of 15 cc / h from the reducing gas introduction section for treatment. When the exhaust gas at the outlet was analyzed by gas chromatography 24 hours and 96 hours after the start of the supply of the exhaust gas, NF ₃ was not detected. In addition, NH ₄ F ・ HF
There was no occlusion due to.

Example 3 A treatment was carried out in the same manner as in Example 1, except that the catalyst used was a nickel layer having a wire diameter of 0.05 mmφ and a length of 40 m (purity: 97 wt%) filled in a 1 cm ³ packed bed. The exhaust gas at the outlet was analyzed by gas chromatography 24 hours and 96 hours after the start of the supply of the exhaust gas, but NF ₃ was not detected.

Example 4 A treatment was performed in the same manner as in Example 1 except that the flow rate of city water from the water inlet pipe was 1 cc / h. After 24 hours and 48 hours from the start of the supply of the exhaust gas, the exhaust gas at the outlet was analyzed by gas chromatography, but NF ₃ was not detected. Also, there was no blockage by NH ₄ F · HF.

Comparative Example 1 A treatment was performed in the same manner as in Example 1 except that the flow of city water from the water introduction pipe was stopped. The pressure on the exhaust gas supply side began to rise 20 hours after the start of the supply of the exhaust gas, and was completely blocked 24 hours later, so the treatment was stopped. When the state was observed, white crystals were clogged about 4 cm below the lower part of the catalyst layer. When this crystal was analyzed, NH ₄ F · H
It turned out to be F.

Comparative Example 2 A treatment was performed in the same manner as in Example 1 except that the temperature of the water inlet tube was maintained at 110 ° C. The pressure on the exhaust gas supply side started to rise 30 hours after the start of the supply of the exhaust gas, and was completely blocked 32 hours later, so the treatment was stopped. Observation of the state revealed that white crystals at the top of the water inlet tube were clogged. Analysis of this crystal revealed that it was NH ₄ F.HF.

Comparative Example 3 A treatment was performed in the same manner as in Example 1 except that the temperature of the catalyst layer was changed to 100 ° C. One hour after the start of exhaust gas supply and 24 hours
After an hour, the exhaust gas at the outlet was analyzed by gas chromatography, and it was found that NF ₃ was hardly decomposed.

[0032]

By using the method and apparatus for removing NF _{3 according to the} present invention, regardless of the change in the NF ₃ consumption rate in the CVD apparatus or the change in the dilution nitrogen at the exit of the CVD apparatus.
NF ₃ can safely react with the reducing gas and be harmed. In addition, it is possible to prevent blockage due to the fluorine compound generated by the reduction reaction by adding water and at the same time prevent the fluorine compound from being mixed into the gas phase, thereby reducing the running cost of the abatement apparatus. it can.

[0033]

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of an abatement apparatus of the present invention.

FIG. 2 is a configuration diagram showing an example of the abatement apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust gas introduction pipe 2 Reducing gas introduction pipe 3 Catalyst packing layer 4 Water introduction pipe 5 Reaction tube main body 6 Double pipe structure outlet 7 Gas discharge pipe 8 Receiver 9 Drain pipe 10 Heater

Claims (9)

[Claims] An exhaust gas containing nitrogen trifluoride and a reducing gas are passed downflow through a catalyst layer heated to 150 to 800 ° C., and then water is dropped to a position below the catalyst layer maintained at 120 ° C. or higher. A method for removing nitrogen trifluoride, comprising supplying nitrogen trifluoride. 2. The catalyst according to claim 1, wherein the catalyst is Fe, Co, Ni, Cu, Z.
3. The trifluoride according to claim 1, wherein the catalyst is a single metal comprising n, Ru, Rh, Pd, Ag, Ir, Pt, and Au, or a solid catalyst containing an element selected from the group consisting of these metal elements. How to remove nitrogen iodide. 3. The method for removing nitrogen trifluoride according to claim 1, wherein hydrogen or ammonia is used as the reducing gas. 4. The method for removing nitrogen trifluoride according to claim 1, wherein the supply amount of water is 0.1 to 10 times the gas capacity of NF ₃ . 5. A reaction tube main body having a catalyst packed bed and a water inlet at a position below the packed bed, an exhaust gas introduction tube containing nitrogen trifluoride upstream of the reaction tube main body, and a reducing agent. A nitrogen trifluoride detoxification device comprising a gas inlet pipe, a drain receiver and a drain outlet pipe on the downstream side, and a catalyst heating heater. 6. The method for removing nitrogen trifluoride according to claim 5, wherein the outlet of the reaction tube main body has a double tube structure. 7. The method for removing nitrogen trifluoride according to claim 5, wherein the outlet pipe of the reaction tube main body is immersed in the liquid in the receiver. 8. The reaction tube body is made of stainless steel, nickel, or Hastelloy.
An apparatus for removing nitrogen trifluoride according to claim 1. 9. The nitrogen trifluoride abatement apparatus according to claim 5, wherein a material other than stainless steel, nickel, Hastelloy, or soft vinyl chloride or nylon is used as a material of the receiver.